Sodium intake as a determinant of urinary prostaglandin E2 excretion

Fluid Intake in the First Week of Life and the Duration of Hemodynamically Significant Patent Ductus Arteriosus in Extremely Preterm Infants

OBJECTIVE

This study aimed to determine the association between daily fluid intake and the duration of hemodynamically significant patent ductus arteriosus (hsPDA).

STUDY DESIGN

This is a retrospective cohort study of extremely preterm infants (<29 weeks) admitted in the Neonatal Intensive Care Unit of the Advent Health for Children from January 2013 to March 2016, if hsPDA was diagnosed in first week of life and serial echocardiograms were available. Diagnosis of hsPDA was based on a scoring system and its duration was estimated from serial echocardiograms. Cohort was divided into two groups based on duration of hsPDA (<1week, group A and ≥1 week, group B). Daily fluid intake was categorized as prescribed and actual. Prescribed volume was ordered by clinicians based on birth weight, not including trophic feeds, intravenous (IV) boluses or transfusions, etc. Actual intake was calculated by the electronic medical records based on daily weights and included all enteral or parenteral fluids. Multivariate analysis was performed to determine an association between total daily fluid intake over the first week of life and the duration of hsPDA. Two groups were compared to observe the difference between prescribed and actual daily fluid intakes.

RESULTS

We enrolled 50 infants in group A and 76 in group B. Infants in group B were of significantly lower gestation and required prolonged ventilation and hospitalization. An association between higher fluid intake in the first 2 days of life and prolonged duration of hsPDA was confirmed by multivariate analysis. Actual fluid intake was significantly higher than prescribed total fluid intake in first 4 days of life for infants in both groups.

CONCLUSION

In extremely preterm infants, higher fluid intake in first 2 days of life is associated with prolonged duration of hsPDA. Actual daily fluid intake can be significantly higher than prescribed daily fluids due to daily weight changes and additional fluid administration.

KEY POINTS

· In preterm infants, actual daily fluid intake may be higher than prescribed volume.. · Higher daily fluid intake in first week of life is associated with prolonged duration of PDA.. · PDA scoring system can be helpful for objective assessment of PDA in preterm infants..

Fluid Intake in the First Week of Life and the Duration of Hemodynamically Significant Patent Ductus Arteriosus in Extremely Preterm Infants

OBJECTIVE

 This study aimed to determine the association between daily fluid intake and the duration of hemodynamically significant patent ductus arteriosus (hsPDA).

METHODS

 This is a retrospective cohort study of extremely preterm infants (<29 weeks) admitted in the Neonatal Intensive Care Unit of the Advent Health for Children from January 2013 to March 2016, if hsPDA was diagnosed in first week of life and serial echocardiograms were available. Diagnosis of hsPDA was based on a scoring system and its duration was estimated from serial echocardiograms. Cohort was divided into two groups based on duration of hsPDA (<1week, group A and ≥1 week, group B). Daily fluid intake was categorized as prescribed and actual. Prescribed volume was ordered by clinicians based on birth weight, not including trophic feeds, intravenous (IV) boluses or transfusions, etc. Actual intake was calculated by the electronic medical records based on daily weights and included all enteral or parenteral fluids. Multivariate analysis was performed to determine an association between total daily fluid intake over the first week of life and the duration of hsPDA. Two groups were compared to observe the difference between prescribed and actual daily fluid intakes.

RESULTS

 We enrolled 50 infants in group A and 76 in group B. Infants in group B were of significantly lower gestation and required prolonged ventilation and hospitalization. An association between higher fluid intake in the first 2 days of life and prolonged duration of hsPDA was confirmed by multivariate analysis. Actual fluid intake was significantly higher than prescribed total fluid intake in first 4 days of life for infants in both groups.

CONCLUSION

 In extremely preterm infants, higher fluid intake in first 2 days of life is associated with prolonged duration of hsPDA. Actual daily fluid intake can be significantly higher than prescribed daily fluids due to daily weight changes and additional fluid administration.

KEY POINTS

· In preterm infants, actual daily fluid intake may be higher than prescribed volume.. · Higher daily fluid intake in first week of life is associated with prolonged duration of PDA.. · PDA scoring system can be helpful for objective assessment of PDA in preterm infants..

Dietary salt induces transcription of the prostaglandin transporter gene in renal collecting ducts

Prostaglandin E(2) (PGE(2)) plays an important role in maintaining body fluid homeostasis by activating its receptors on the renal collecting duct (CD) to stimulate renal Na(+) and water excretion. The PG carrier prostaglandin transporter (PGT) is expressed on the CD apical membrane, where it mediates PG reuptake as part of the termination of autocrine PG signaling. Here we tested the hypothesis that dietary salt loading regulates PGT gene transcription in renal CDs. We placed green fluorescence protein (GFP) under control of 3.3 kb of the mouse PGT promoter and injected this construct into the pronuclei of fertilized FVB mouse eggs. Four of thirty-eight offspring were GFP positive by genotyping. We extensively characterized one (no. 29) PGT-GFP transgenic mouse line. On microscopic examination, GFP was expressed in CDs as determined by their expression of aquaporin-2. We fed mice a low (0.03% NaCl)-, normal (0.3% NaCl)-, or high-salt (3% NaCl) diet for 2 wk and quantified CD GFP expression. The average number of GFP-positive CD cells per microscopic section varied directly with dietary salt intake. Compared with mice on the control (0.3% sodium) diet, mice on a low-sodium (0.03%) diet had reduced numbers of GFP-positive cells (71% of control, P < 0.001), whereas mice on a high-sodium (3%) diet had increased numbers of GFP-positive cells (139% of control, P < 0.001). This increase in apparent CD PGT transcription resulted in a 51-55% increase (P < 0.001) in whole kidney PGT mRNA levels as determined by real-time PCR. The regulation of PG signal termination via reuptake represents a new pathway for controlling renal Na(+) balance.

Prostanoids and aldosterone-induced mild experimental hypertension in rats

The goal of this study was to determine the role of prostanoids in a new model of mineralocorticoid-dependent hypertension induced by the subcutaneous infusion of aldosterone (1 micrograms/hr) to normal male Sprague-Dawley rats. This regimen caused a mild and gradual increase in systolic pressure over a period of 4 weeks (113 +/- 1 vs. 137 +/- 3 mm Hg) and was associated with an increase in the in vivo formation of prostaglandins I2 and E2 and of thromboxane A2 in the kidney. High sodium intake induced a fall in the urinary levels of prostaglandin E2 and a rise in the arterial pressure of control rats (126 +/- 1 vs. 113 +/- 1 mm Hg) but did not influence aldosterone-induced hypertension. Indomethacin (3.0 mg/kg/day) caused a profound inhibition of the in vivo synthesis of prostaglandin I2 and thromboxane A2 without modifying the renal production of prostaglandin E2. Although indomethacin exerted no effect on aldosterone-induced hypertension in rats fed a normal diet, it caused a further rise in systolic pressure in aldosterone-treated rats fed a high sodium diet (157 +/- 6 vs. 140 +/- 4 mm Hg). The results of this study in a model of aldosterone-induced mild hypertension in the rat indicate that 1) aldosterone exerts a stimulatory effect on the renal synthesis of prostanoid, particularly prostaglandin E2; 2) thromboxane A2 and prostaglandin I2 do not seem to play a role in aldosterone-induced hypertension under conditions of normal dietary salt intake, whereas the role of prostaglandin E2 is unclear; 3) there is enough sodium in a normal diet to allow for the maximal expression of the hypertensive effect of aldosterone; 4) prostaglandin I2 seems to play a significant role in modulating the cardiovascular impact of a high sodium diet in aldosterone-treated rats; and 5) the renal biosynthesis of prostaglandin E2 is particularly resistant to the inhibitory effect of indomethacin in vivo.

Effects of acute and chronic dosing of NSAIDs in patients with renal insufficiency

Administration of nonsteroidal anti-inflammatory drugs (NSAIDs) to patients with chronically impaired renal function has been reported to cause abrupt and sustained reductions in renal plasma flow (RPF), glomerular filtration rate (GFR), and solute and water excretion in association with decreased renal prostanoid production. However, the time course of these acute effects and whether they are sustained during chronic exposure to the NSAIDs are unknown. Accordingly, using standard clearance and balance techniques, we investigated the effects of acute (zero to four hours) and chronic (five days) oral administration of two different NSAIDs on renal function in patients with stable, mild to moderate chronic renal insufficiency (CRI) and in normal subjects. In patients, acute oral administration of ketoprofen (K) and indomethacin (I) resulted in significant decreases in GFR (K: from 36 +/- 3 to 20 +/- 4 ml/min, P = 0.001; I: from 37 +/- 6 to 30 +/- 7 ml/min, P = 0.032; in RPF (K: from 194 +/- 21 to 146 +/- 21 ml/min, P = 0.002; I: from 222 +/- 33 to 147 +/- 18 ml/min, P = 0.016); and in urinary PGE2 excretion (K: from 0.60 +/- 0.25 to 0.08 +/- 0.02 ng/min, P = 0.05; I: from 0.34 +/- 0.06 to 0.18 +/- 0.06 ng/min, P = 0.042). Fractional excretion of sodium chloride and fractional free water clearance (CH2O/CIn) also decreased significantly after both agents. In normal subjects, GFR and RPF were not significantly decreased after acute dosing, whereas urinary PGE2 and fractional excretions of NaCl and free water decreased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Self-selected vs. controlled diet as a baseline for human studies: effects of nutrient intakes on blood pressure and on constituents of blood and urine

This study demonstrates that a three-week stabilization period, in which all subjects eat an identical diet, produced a more uniform but different baseline of metabolic parameters than the subject's self-selected or "habitual" diets. Subjects required more food energy to maintain initial body weights during the stabilization period than when they ate their reported self-selected diets; average intakes of almost all nutrients were higher from the stabilization than from the self-selected diet. The switch to the stabilization diet produced small but significant reductions in blood pressure, in some serum enzymes, urine volume, and sodium; and statistically significant increases in serum LDL cholesterol, potassium, aldosterone, protein, albumin, phosphorus, BUN, and in urine potassium. The findings indicate that results must be interpreted with caution from studies in which the baseline for measuring metabolic variables is established by feeding subjects a standardized diet that differed markedly from their regular, self-selected diets.

Effects of prostaglandin synthesis inhibitors on the renin-angiotensin system and renal function

Equal doses (8 mg/kg) of the nonsteroidal antiinflammatory drugs indomethacin, naproxen, and sulindac and a large dose of sulindac (32 mg/kg) were administered intragastrically to conscious rats after a normal sodium diet, furosemide stimulation, and a low sodium diet for 8 days. Indomethacin, naproxen, and the high dose sulindac (32 mg/kg) decreased urinary prostaglandin E2 excretion significantly under all experimental conditions. Sulindac (8 mg/kg) suppressed prostaglandin E2 excretion after the normal and low sodium diets but not after furosemide stimulation. Indomethacin decreased plasma active renin levels under all three experimental conditions. In rats receiving a normal sodium diet, indomethacin did not affect free water clearance or renal function; however, after furosemide stimulation or a low sodium diet, indomethacin caused a significant reduction of free water clearance and glomerular filtration rate. Naproxen and sulindac (8 mg/kg) did not suppress active renin under any of the experimental conditions. However, naproxen and sulindac caused a significant reduction in free water clearance and glomerular filtration rate after furosemide stimulation and a low sodium diet. Indomethacin, naproxen, and the high dose sulindac suppressed renal prostaglandin E2 excretion under all experimental conditions. Renal prostaglandin E2 does not appear to be necessary for active renin secretion. Indomethacin is the most potent inhibitor of active renin and, therefore, most likely to cause hyporeninemia. Volume depletion appeared to sensitize the kidney to the adverse effects of nonsteroidal antiinflammatory drugs.

The influence of prostaglandin E2 and indomethacin on the renal corticomedullary solute gradient in the rat

The renal corticomedullary solute gradient and the urinary excretion of fluid and solute were determined during a saline infusion in anaesthetized and conscious rats. In the anaesthetized group the influence of PGE2 (100 ng min-1) given by a local renal infusion was investigated. In the conscious group (where prostaglandin synthesis does not contribute to renal blood flow) the effect of indomethacin (i.v. 10 mg kg-1) was determined. Following PGE2 infusion the corticomedullary gradient for sodium was depressed, equalizing the sodium concentration between the papilla tip and the final urine. Sodium output and urine flow were elevated, but both urinary and gradient changes could be dissociated from any increase in renal blood flow, assessed by PAH clearance. Following treatment with the prostaglandin synthetase inhibitor indomethacin in the conscious rat, the corticomedullary osmotic gradient was elevated while the urine flow was reduced. This increase in the gradient produced by indomethacin was, however, found to be independent of the decrease in urine flow. The results of the present experiments are consistent with the hypothesis that prostaglandin synthesis helps to determine the renal corticomedullary osmotic gradient, and does so by a mechanism unlikely to involve changes in renal blood flow or tubular flow rate: a permeability hypothesis is proposed.

Prostaglandin E2 excretion, urine flow and papillary osmolality during saline or dextrose infusion in the conscious rat

Conscious rats received infusions at 5.8 ml./hr of either 0.9% NaCl or 5% dextrose, via a tail vein, for 6 hr. During this infusion period, urine was collected from the animals, and the urine volume, sodium concentration and immunoreactive PGE2 were determined. Urine flow in both groups was stable during the 2-6 hr period of the infusion and was not significantly different between the two groups. Sodium output was also stable over the 2-6 hr infusion period but obviously the output of the saline-infused group was higher than that of the dextrose-infused group. Urinary PGE2 output was not significantly different between the groups in the 2-4 hr period (79.4 +/- 8.6 p-mole/2 hr in the saline-infused group, 82.1 +/- 5.7 p-mole/2 hr in the dextrose-infused group). In the 4-6 hr period, PGE2 output remained at this level (82.0 +/- 7.8 p-mole/2 hr) in the dextrose-infused group, but fell significantly (to 53.7 +/- 5.0 p-mole/2 hr) in the saline-infused group. In separate groups of animals which received saline or dextrose infusions as above, renal papillary osmolality was determined. The osmolality was significantly (P less than 0.001) higher in the saline-infused group. It is concluded that renal PGE2 synthesis is unlikely to be directly involved in sodium homeostasis and that PGE2 synthesis as measured by urinary PGE2 excretion is not controlled by the papillary osmolality.

Renal effects of pinane-thromboxane A2 and indomethacin in saline volume-expanded spontaneously hypertensive rats

In 6-week old spontaneously hypertensive rats (SHR), indomethacin (5 mg/kg i.v.) and pinane-thromboxane A2 (PTA2) (50 micrograms/kg per h i.v.) a thromboxane A2 (TXA2) antagonist as well as a TXA2 synthetase inhibitor, resulted in natriuresis accompanied by an increase in p-aminohippuric acid and inulin clearances. Indomethacin acted as an antidiuretic in 6 week Wistar-Kyoto rats (WKY). PTA2 did not alter renal functions in either 6 week WKY and 18 week SHR. Basal urinary excretion of TXB2 (UTXB2V) was greater in 6 week SHR than in 6 week WKY and 18 week SHR, and that of 6-keto-PGF1 alpha (U6-keto-PGF1 alpha V) did not differ among these strains. Thus, U6-keto-PGF1 alpha V/UTXB2V was lower in the 6 week SHR. Basal urinary excretion of PGE (UPGEV) was much greater in 18 week SHR than in the 2 other groups. In the 6 week SHR, PTA2 decreased UTXB2V and increased U6-keto-PGF1 alpha V without affecting UPGEV, and indomethacin reduced UTXB2V more markedly than did U6-keto-PGF1 alpha V and UPGEV. Thus, both PTA2 and indomethacin increased U6-keto-PGF1 alpha V/UTXB2V in the 6 week SHR. These findings indicate that a disequilibrium in the biosynthesis of vasoconstrictive TXA2 and of vasodilator PGI2 may be involved in water and sodium retention in SHR during the developmental phase of hypertension.

Effect of salt on prostaglandin metabolism in hypertension-prone and -resistant Dahl rats

The effect of high salt intake on vascular and renomedullary prostaglandin (PG) synthesis was compared in Sprague-Dawley and salt-sensitive (S) and -resistant (R) Dahl rats. Animals were given a diet containing either 0.6% or 8% NaCl starting at 5 weeks of age, and were sacrificed 6 weeks later. Systolic blood pressure of S rats increased to 220 +/- 7 mm Hg but was unaffected in R and Sprague-Dawley rats. Prostaglandin synthesis was studied in aortic rings and renomedullary microsomes using 14C-arachidonate as substrate. [3H]PGE2 degradation was measured in the renocortical cytosol. In Sprague-Dawley and R rats, aortic PGI2 synthesis was not affected by high salt intake, while a significant increase compared to animals on 0.6% NaCl (from 608 +/- 84 to 992 +/-108 pmoles/60 min, p less than 0.05) was noted in S rats. Enhancement of PGI2 synthesis in S rats may be secondary to the hypertension. Salt-loading consistently stimulated renomedullary PGE2 synthesis in all three animal groups. S rats, however, had the lowest PG synthesis in renal medullas compared to Sprague-Dawley and R rats when placed on either diet. Thus, even after 6 weeks on high salt, S rats did not reach the levels of PGE2 synthesis seen in R or Sprague-Dawley rats on regular diet. The activity of cortical 15-hydroxyprostaglandin dehydrogenase was increased by salt-loading in S and Sprague-Dawley, but not in R rats. R rats had lower dehydrogenase activity than the other two groups when placed on either diet. The observed differences in PG synthesis and catabolism will tend to maintain the net output of renal PGs highest in R and lowest in S rats. These differences correlate with the reported differences in renal papillary flow between these two rat strains and may be relevant to their susceptibility or resistance to hypertension in response to salt.